Mutualistic association of rotifer Philodina roseola with the branchiuran fish ectoparasite Argulus bengalensis at its embryonic stage

Several rotifers includingPhilodinaspp. are well known to make commensal and parasitic associations with different animals. The present investigation was carried out to decipher the relationship ofPhilodina roseolawith a piscine ectoparasiteArgulus bengalensisin its embryonic stage. Mechanical removal of the symbiontP. roseolafrom the argulid egg strips resulted in the complete (100%) failure in hatching. SeveralP. roseolaindividuals were found to feed on the solidified jelly coat of the eggs enabling the larvae to emerge under both laboratory and field conditions. Under the laboratory condition, the experimental removal ofP. roseoladid not affect the embryonic development, but it rendered the jelly coat intact; therefore, the larvae were unable to make hatching furrow and subsequently died. The results of our experiments thus prove this service-resource relationship to be a mutualism. Although the association is facultative forP. roseola, it is obligatory forArgulusspp. An act of intervention in this relationship thus offers a promising control of argulosis.